1. Technical Field
The present invention relates to an information processing apparatus having an information storage device with a driving part such as a magnetic disc device, a power saving control method of monitoring an access state to the information storage device and shifting the present mode to a power saving mode, and a recording medium such as a magnetic disc or a semiconductor storage device in which a power saving control program is stored.
2. Description of Related Art
A large-capacity information storage device such as a magnetic disc device, a floppy disc device or a photomagnetic disc device employs a single or a plurality of discs as a recording medium and includes a driving part such as a motor that makes the disc rotate and a head positioning actuator that conducts the read/write of data with respect to the disc. The large-capacity information storage device is applied to external storage means of various information processing apparatuses. Also, the magnetic disc device is representatively classified into the IDE (Integrated Drive Electronics) type and the SCSI (Small Computer System Interface) type as an interface type. Further, in order to improve the efficiency of utilization of energy regarding an information processing apparatus, there has been proposed various power saving control means which change over the operating voltage, change over the operating clock frequency, or the like. In addition, the information storage device includes a power management function for reducing the power consumption by transition to the operating mode in accordance with the operating state of the main unit of computer system.
For example, in a structure including an HD controller 52, a device driver 53, and a BIOS (Basic Input/Output System) 54 with respect to a firmware (including a magnetic disc device HDD) 51 shown in FIG. 10, the power management function of this type is realized mainly by the firmware 51, by the firmware 51 and the device driver 53, or by the combination of the firmware 51 with the BIOS 54.
FIG. 11 is an explanatory diagram showing the operating mode of the information storage device, in which FIG. 11(A) shows a state transition and shows a case in which a mode is changed over such that the present mode is an active mode during a period where the read/write of the data is conducted in accordance with a request from the main unit of computer system with respect to the magnetic disc device HDD as the information storage device, the present mode is shifted to an idle mode if there is no access to the magnetic disc device HDD after a predetermined period of time elapses, the mode is then shifted to a standby mode if there is still no access for another predetermined period of time, and the mode is then shifted to a sleep mode if there is still no access after elapse of yet another predetermined period of time. Then, in the modes other than the active mode, the mode is shifted to the active mode in response to an access request from the computer body.
FIG. 11(B) shows a relationship between a period of time where the magnetic disc device HDD is returned to the active mode and the power consumption. The active mode is a state in which the motor is rotated as the driving part of the magnetic disc device HDD to conduct the read/write of data. The active mode is largest in power consumption of all the modes. Also, the idle mode is a state in which there is no access from the main unit of computer system to reduce the power consumption by conducting the power saving control. The idle mode is returned to the active mode in a short period of time in response to the access request from the main unit of computer system. Further, the standby mode is to conduct the power saving control so as to further reduce the power consumption, and a transition time period of from the standby mode to the active mode in response to the access request from the main unit of computer system is slightly long. Further, the sleep mode is to stop the motor of the magnetic disc device HHD so as to further reduce the power consumption, and a transition time period of from the sleep mode to the active mode in response to the access request from the main unit of computer system is longer since the sleep mode includes the initialization of the hardware and so on.
For example, as shown in FIG. 12(A), in the case where the magnetic disc device HDD is accessed periodically, the magnetic disc device HDD shifts from an active mode a to an idle mode b after a predetermined time period elapsed since the completion of access and shifts to a standby mode c after a further predetermined time period elapsed as shown in FIG. 12(B). If the magnetic disc device HDD is accessed during the standby mode c, the magnetic disc device HDD shifts from the standby mode c to the active mode a. In the case where the magnetic disc device HDD is not accessed further for a long time during the standby mode c, the magnetic disc device HDD shifts to a sleep mode d. The above power management control makes it possible to reduce the power consumption as compared with a case where the active mode continues.
Also, FIG. 12(C) shows a periodic access state as in FIG. 12(A). In contrast to this, as shown in FIG. 12(D), it is considered that a shortened period of time of the idle mode b where the magnetic disc device HDD is shifted from the active mode a to the standby mode c reduces the power consumption further. However, there has not yet been known how to realize such a power saving mode.
As described above, in the case where access is periodically made to the information storage device from the main unit of computer system, if the period is found out, it is unnecessary to continue the active mode and the idle mode for a constant period of time during the time period where there is no access. As shown in FIG. 12(D), after the access has been completed, the magnetic disc device HDD is set to a power saving mode where the period of the idle mode b is shortened and then shifted to the standby mode, thereby the power consumption can be further reduced.
However, the power management function of the magnetic disc device HDD is mainly realized by the firmware 51, and in order to conduct the power management control as the one described above, it is necessary to correct the firmware 51. In this case, since there is restriction in code size of the firmware 51, only a slight function can be added. Also, since there is no margin of the code size, it is generally difficult to correct the code. Further, even if the firmware 51 can be corrected, it is necessary to correct the firmware 51 so as to be adaptive to the magnetic disc device HDD, and there arises a problem that an erroneous correction may occur in this point.
Also, there has been known a method in which an access frequency is obtained as the pattern of access to the magnetic disc device HDD, and a power supplied to structural elements is reduced when the access frequency is equal to or less than a threshold value (See Japanese Patent Application Laid-Open No. Hei 9-17099, for example). However, the access frequency to the magnetic disc device HDD fluctuates during a process of executing various programs in the main unit of computer system. Also, the access frequency is shown in the form of temporal average in the case of access having an ideal periodicity as shown in FIGS. 12(A) and 12(C), and therefore stable power saving control is difficult.